HIAF-BRing束团合并过程中的束流负载效应模拟

强流重离子加速器HIAF-BRing在加速完成后进行束团合并，为研究BRing中的束流负载效应对束团合并的影响，对238U35+束流进行了粒子跟踪模拟。模拟结果显示，在束团合并过程中，束流负载效应引起束团长度和束团中心位置的振荡，导致束流动量分散和束团长度的增长。束团合并过程中尾场电压以及不同束团间尾场的耦合导致的势阱畸变，是引起束团长度和束团中心振荡及束流发射度增长的原因。为了降低束流负载效应的影响，采用多谐波前馈系统进行补偿，达到了补偿束团合并过程中的束流负载效应的目的，从而确保了BRing中引出束流的品质，同时根据模拟结果确定了前馈系统需要覆盖的频率范围和需要补偿的最大尾场电压。

Simulation Study of the Beam Loading Effects During the Bunch Merging in HIAF-BRing

In the booster ring (BRing) of the High Intensity heavy-ion Accelerator Facility (HIAF), the multi-bunch should be merged into single bunch after the acceleration. To study the influence of the beam loading effects during the bunch merging, the simulations of particle tracking with 238U35+ beam are carried out. According to the simulation results, during the bunching merging, the beam loading effects can result in the growth of the momentum spread and the bunch length as well as the oscillation of the bunch length and the bunch center. The potential well distortion induced by the wake voltage and wake field coupling during the bunch merging are the reasons why the bunch center oscillates and the emittance of the beam grows. To reduce the influence of the beam loading effects, the multi-harmonic feed-forward system is employed to compensate the wake voltage. With the feed-forward system, the beam loading effects can be compensated during the bunching merging. The feed-forward system is able to guarantee the high quality of the beam for extraction in the BRing. The frequency range to be covered and the largest wake voltage to be compensated by the feed-forward system are determined according to the simulation results.